Posted on 02/17/2017 5:09:30 PM PST by nickcarraway
Officials at Lake Oroville reduced the rate of water release once again Friday as workers continued make repairs to a damaged spillway and clear debris from a hydroelectric plant.
State Department of Water Resources engineers will decrease the flow of water in the Oroville Dam's main spillway from 80,000 cubic feet per second to 60,000 by Saturday morning, giving crews space to dredge debris from a pool at the bottom of the spillway, said DWR acting director Bill Croyle.
Engineers had been pumping water out of the lake at 100,000 cfs for several days to make room for incoming storm runoff and to keep the lake from overflowing like it did over the weekend. That overflow badly eroded an emergency spillway and sent debris flowing into a pool at the bottom, forcing the closure of an underground hydroelectric plant.
“This reduction in flow will allow us to work on the debris pile in the spillway,” Croyle told reporters at a news conference. He estimated that 150,000 cubic yards of sediment and debris were in the pool.
The other focus by workers at the dam is the eroded emergency spillway, Croyle said. Rain began falling again in the area on Thursday and it’s not expected to stop until the middle of next week at the earliest.
The heaviest showers are expected Monday and could drop up to 10 inches of rain onto the mountains and foothills that drain into the reservoir, the National Weather Service said.
The storms aren't likely to produce enough runoff to exceed the lake's capacity, Croyle said.
Hundreds of thousands of tons of rocks and concrete slurry have been dropped into four fissures that threatened a retaining wall of the emergency spillway on Sunday. They were 50%, 75%, 90% and 100% full, respectively, Croyle said.
(Excerpt) Read more at latimes.com ...
TruthInThoughtWordAndDeed, ctdonath2
On what do y’all base your estimations?
Expected inflow over the next week, vs feasible outflow through the main and emergency spillways?
Yes, inflows will swamp outflows. The crew working at the dam know that the situation is hopeless. The media are suppressing the truth.
First the emergency spillway. That will fail structurally within hours of the time water begins flowing over it. Then, when the concrete breaks up, the flow volume will increase and start digging at the dam’s foundations.
Of note, people are giving the Oroville Dam reviews on Google. Pretty funny in a dark/offensive humor way.
https://www.google.com/search?q=oroville+dam#fpstate=lie
Yes, I am an engineer. The emergency spillway will fail structurally within hours of the time water begins to overflow it. That will lead to a cascading failure of other parts of the dam.
bkmrk
https://livestream.com/KRCR/events/3724366
Local radio station found on this thread, h/t 4liberty & keat:
http://www.freerepublic.com/focus/f-news/3525597/posts?page=1#1
Local radio station:
http://www.freerepublic.com/focus/f-news/3525597/posts?page=46#46
Well, let’s run some numbers:
From Wikipedia, Lake Oroville catchment basin = 3950 sq. miles, or, 2,528,000 acres.
10” of (forecast) rain over that area is 2,106,666 acre-feet of water.
If 1/2 makes it to the lake by next Tuesday, that’s 1,053,333 acre-feet added to the lake.
Capacity of the lake is said to be 3,537,577 acre feet.
How far will it be down by Tuesday?
I’ll conservatively assume 8 days discharge at 85,0000,000 cfs drain rate, and adjust by -10,000 cfs for average continued inflow, which equals roughly 1.72 acre ft / sec for 8 days, or, 1.72 x 8 x 24 x 60 x 60 = 1,118,864 acre feet drained in 8 days. I suspect the real number will be better, by the time the new water really gets going, however, my inflow # is just a guess, as I really don’t have a good source of that information.
OTOH, multiple sources (LA Times, etc.) say the DWS is shooting for 1 million acre-feet reserve capacity, which is a little under my estimate, and seemingly dangerously close to my projected inflow. Plus, as best as I can tell from published graphs, Lake Oroville dropped roughly 100,000 acre-feet per day the 1st 3 days after the peak level was hit. Again, that is poorer than my estimate, and would come in well under 1 million acre-feet reserve capacity even if maintained, which I suspect it is not.
Recall that last week, DWS thought they could squeak by, but then the rains persisted longer than expected, AND, DWS shut down the main spillway when the major damage became apparent, after having already reduced discharge to buy time for the salmon at the Feather River Hatchery.
It could be close, early next week, esp. if this next system melts a lot of snow.
Looking at it another way, the system last week dumped 20” of rain, swamping, but not drastically so, the roughly 700,000 acre-feet reserve capacity available when the “big water” began to arrive. This next storm is expected to bring 10” of rain, again leading to an expectation of squeaking by.
It seems like dicey stuff, to me. If MO Nature throws CA a curveball, with either peak inflow rates of ~190,000 cfs (as with last week’s storm) or if the storm system unexpectedly stalls, at least that emergency spillway will fail.
In that case, if the bedrock below the emergency spillway is poor, the new channel may cut more downward than over to the main spillway and then the side of the dam. There will still be serious flooding downstream, of course.
If that bedrock is “good”, then lateral growth of the failure will approach the dam. My guess is that this might take a few days, and by then the “pressure” will be off of the lake. But, at that point, such serious damage will have been done that repair or mitigation is probably a futile attempt, until summer arrives. In fact, in this case, I would almost think that deliberate blasting of a deep channel through the emergency spillway would be the best bet, so as to save the dam itself while allowing a few months of moderate floods downstream, rather than have a final catastrophic “surge” sent downstream by a main dam failure.
Any way you look at it, if this next storm causes inflows like last week’s storm, it’s a big dam problem.
See my post #28. My guesstimate (also an engineer) is that most likely they squeak by. But, it’s really dicey...
Downstream levees are also a big worry.
http://www.sacbee.com/news/state/california/water-and-drought/article133326709.html
One more article:
That main spillway is a big structure itself: 178 ft. wide and 3000 ft. long. That helps give (at least me) a better perspective of the violence of the water when it hits that damaged area.
Thanks for the details !
Related; I saw this announcement on the NOAA weather site:
“WSR-88D Radar Outage Notification / Free Text Message Issued by errNWS Current Version | Previous Version | Text Only | Print | Product List | Glossary OnVersions: 1000 NOUS66 KSTO 151632 FTMBBX Message Date: Feb 15 2017 16:35:06 KBBX radar in Oroville will be down for maintenance from about 17z to 21z today (900AM PST to 100PM PST). Thank you for your patience.”
I wonder about this...
Thank you for your perspective.
Another problem is that parts of some roads are beginning to get washed out. IF they have to evacuate again that will be a real nightmare.
I suggest that the big danger is erosion on the emergency spillway, with water eventually going around the barrier. That will cause a catastrophic event that leaves the dam untouched but allows huge flooding.
Model Dam Fail
The storms aren’t likely to produce enough runoff to exceed the lake’s capacity.
Funny- Someone here on FR did calc a few days ago. Based upon 12 inches of rain over 10 days, and the total watershed of the Feather River—which inflows to Oroville Dam, he said the water could be 13 feet above the emergency spillway.
“Engineers had been pumping water out of the lake at 100,000 cfs”
Can pumps, even a bunch of them, transfer that much water per second?”””
More fake news & stupid news from our media. I am convinced that combined total aggregate IQ of all the media in the USA is about 122.
They are not pumping water down the spillway——They are opening up the outflow weirs & letting the water remove itself. This is a SPILLWAY——no pumps seem to be visible or involved.
Can you pour water out of a bucket? Can you pour it slowly—or faster—or dump it? Same theory.
I do not disagree with any of your calculations. The Feather River starts in the Sierra Nevada & comes a long way with lots of watershed before it gets to Oroville Dam.
IF there is serious flooding, it will last more than ‘a few months’ & the entire rice crop & thousands of acres of alfalfa will be wiped out. The farms & ranches in the Sacramento Valley are BELOW sea level, depending on the levees to keep they dry. Dairy farms, horse operations, and other crops grown. The face horse California Chrome came from Yuba City area.
IF anyone here remembers the 1986 & 1996 floods into Marysville & Yuba City, they were pretty damaging—and the high water mark on buildings in Yuba City were over 10 feet above he ground. I saw that for myself, when I lived just east of Yuba City in Grass Valley.
The storms aren't likely to produce enough runoff to exceed the lake's capacity, Croyle said.
I think you are wishful thinking there, chief.
Ten inches in ONE freaking day means you will have feeder creeks overflowing their banks.
Maybe this season will have an effect on the 2018 elections in Sacramento and get rid of some of the real dumb asses in the legislature.
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